Панго

Pangois an open-source library for laying out and rendering Unicode text. It appears to sit on top of the GTK display library and can specify either Cairo or Win32 (Uniscribe) rendering back-ends. It offers a more complete solution than Uniscribe and appears to be very well designed and implemented. However Pango is UTF-8 based so this may be a consideration if the rest of your application is UTF-16.

QT Rendering

Харфбуц

ИЦУ

Apple Type Services For Unicode Imaging (ATSUI) is Apple's own version of Uniscribe, although it appears to be higher-level than Microsoft's effort. A brief look at the documentation for ATSUI indicated a much easier-to-use design, and substantially better documentation than Microsoft had managed for Uniscribe.